This invention relates to methods and apparatus for projecting molten particles, and, more particularly, to methods and spray apparatus for providing a surface coating of plastic or the like on a desired object.
In the operation of existing devices of the character known as powdered flame spray guns, a powdered thermoplastic is heated to its melting point, such as by an oxy-propane flame. The resultant material is then propelled against the article to be coated by means of a jet of propelling air, whereupon the molten material fuses to form the desired surface coating.
Serious problems have been associated with such techniques in achieving the proper temperature and manner of mixture of the various spray ingredients, and in the manner of projecting the melted plastic against the article.
In some apparatus, for example, problems have been encountered in avoiding the clogging of the nozzle by the powdered feedstock. Yet another drawback of other processes was the need for oxygen to effect an oxy-propane melting flame in an effort to reduce the likelihood of overheating the powdered material in the gun.
Still a further difficulty with the prior methods and apparatus was in maintaining a critical relationship between the various parameters which made the difference between a successful coating operation and a failure.
For example, in a typical flame spray gun, various flows of materials interact such as a gas flow providing the heat for the process, a source of oxygen flow for supporting the flame, a propelling gas stream for projecting the molten material against the article, and a moving powderized plastic stream. It can readily be appreciated that the rate of movement of such materials, and the order and manner in which they interact with one another can be critical to the successful operation of the device. Accordingly, prior apparatus was plagued with requirements for continuely making fine adjustments of the various parameters to achieve a proper mixture. As but one example, the angle at which the flow of the combustible gas mixed with the other ingredients of the process as well as the flow rate thereof appeared to be quite sensitive in affecting the outcome of the process. If these relationships were not in the proper balance, the spray gun would fail to remain ignited during the application process or, in the alternative, would not operate with maxmimum efficiency resulting from poor combustion.
Accordingly, a method and apparatus for projecting molten particles was desired which was simple in construction and ease of operation and which effected an intermixing of components of the spray in an open chamber wherein the need for a source of substantially pure oxygen was further obviated. These previously described problems associated with previous methods and apparatus are overcome by the present invention and a novel method and apparatus for applying powdered flame sprays is supplied.